1. Field of the Invention
This invention relates to universal joints. In one aspect, this invention relates to rotary joints which permit rotary motion at varying angles. In one aspect, this invention relates to rotary joints providing interior fluid communication from one side of the joint to the other side of the joint. In one aspect, this invention relates to rotary joints for use in steerable drilling systems for subterranean drilling.
2. Description of Related Art
Typically, a wellbore is a substantially straight vertical hole. However, there are times when a drilling operator may desire to drill a non-vertical hole off the vertical wellbore, for example to enable drilling in a substantially horizontal direction into an oil or gas bearing formation. Directional drilling systems are used to control the direction of subterranean drilling systems between vertical and off-vertical as well as side-to-side directions. Directional drilling systems that allow steering while drilling typically fall into two categories: push-the-bit and point-the-bit systems, classified by their mode of operation. Push-the-bit systems operate by applying pressure to the side walls of the formation containing the well. Point-the-bit systems operate by aiming the drill bit in the desired direction, causing deviation of the well as the bit drills the bottom of the well.
Rotary steerable drilling systems used to control the direction of subterranean drilling systems between vertical and off-vertical as well as side-to-side directions allow steering of the drill bit while continuously rotating the drill string and drilling the wellbore.
One commonly used point-the-bit rotary steerable drilling system employs a bendable rotary drive shaft inside a non-rotating housing, an example of which is taught by U.K. Patent No. GB 2,172,324. As described therein, a control module comprising a casing having a bearing at each end thereof for supporting the drive shaft as it passes through the casing is utilized. Four flexible bags located in the annular space between the drilling string and the casing control the direction of the drilling by applying a radial force to the drive shaft such that the drive shaft is displaced laterally between the bearings to provide a desired curvature of the drive shaft. U.S. Pat. No. 6,244,361 to Comeau et al. teaches a deflection device consisting of two eccentric rings that is axially located between a first support location and a second support location of a rotatable drive shaft within a non-rotating housing for bending the drilling shaft between the first location and the second location.
U.S. Pat. No. 6,092,610 to Kosmala et al. teaches an actively controlled rotary steerable drilling system for directional drilling of wells having a tool collar rotated by a drill string engaged in well drilling. The bit shaft is supported by a universal joint within the collar and rotatably driven by the collar. To achieve controlled steering of the rotating drill bit, orientation of the bit shaft relative to the tool collar is sensed and the bit shaft is maintained geostationary and selectively axially inclined relative to the tool collar during drill string rotation by rotating it about the universal joint by an offsetting mandrel that is rotated counter to the collar rotation and at the same frequency of rotation. An electric motor provides rotation to the offsetting mandrel with respect to the tool collar and is servo-controlled by signal input from position sensing elements. A brake is used as necessary to maintain the offsetting mandrel and the drill shaft axis geostationary. While the use of universal joints between the deflecting device and the upstream driving shaft significantly reduces bending of the shaft and the inherent stresses/fatigue failure risks resulting from a bent shaft, universal joints are bulky and difficult to seal against high pressure drops between the inside and outside of the shaft. In addition, these joints, having only two to four points of connection, are only symmetrical about one or two axes and, thus, do not provide smooth and uniform transfer of rotational speed and torque.
U.S. Pat. No. 6,837,315 to Pisoni et al. describes a rotary steerable drilling tool having a tool collar, a bit shaft supported within the tool collar for pivotal movement about a fixed position along the bit shaft, and a variable bit shaft angulating mechanism, which includes a motor, an offset mandrel, and a variable offset coupling, disposed within the interior of the tool collar. The tool further includes a torque transmitting coupling adapted to transmit torque from the tool collar to the bit shaft at the fixed position along the bit shaft.
A bottom hole assembly for drilling a deviated borehole is taught by U.S. Pat. No. 6,581,699 to Chen et al. which utilizes a positive displacement motor or a rotary steerable device having a substantially uniform diameter motor housing outer surface without stabilizers extending radially therefrom. In the case of the positive displacement motor, the motor housing may include a fixed bend therein between an upper power section and a lower bearing section. The bit is rotated at a speed of less than 350 rpm and has a gauge section above the bit face such that the total gauge length is at least 75% of the bit diameter and at least 50% of the total gauge length is substantially full gauge. The axial spacing between the bend and the bit face is controlled to less than twelve times the bit diameter.
U.S. Pat. No. 7,234,543 to Schaaf teaches a system for directional drilling which includes a biasing subsystem configured to control a tendency of a bottom hole assembly during drilling of the borehole and a continuously variable transmission coupled by an output shaft to the biasing subsystem such that the continuously variable transmission is configured to control relative rotation of one or more components of the biasing subsystem during the drilling operation.